Topsoil restoration is a key step in the ecological restoration of the dump of open pit coal mine, and the thickness of soil cover directly affects plant growth and reclamation cost. In order to study the influence of the thickness of soil cover on soil water infiltration and plant water utilization in open pit mine dump, indoor soil column simulation test was adopted in this study. Five cover thicknesses of 10 cm, 20 cm, 30 cm, 40 cm and 50 cm were set up, and vertical infiltration test and indoor pot test (corn) were conducted, respectively. Combined with hydrogen and oxygen isotope stable tracing technology, soil infiltration and water use characteristics of corn with different cover thicknesses were studied to screen the optimal soil cover thickness for the waste dump in the region. The results showed that:the initial infiltration rate with a soil cover thickness of 10~30 cm (27.05~33.02 mm/min) was significantly higher than that with a soil cover thickness of 40~50 cm (21.59~24.89 mm/min) (p<0.05). The stable infiltration rate increased with the increasing of soil cover thickness. When the soil cover thickness was greater than 40 cm, the infiltration rate remained at about 3 mm/min with the increasing of the soil thickness. The infiltration process of gangue layer was greatly affected by the soil cover thickness. When the thickness of overlying soil was greater than 40 cm, the infiltration rate of gangue layer was basically stable at the infiltration rate of soil layer interface. The intersection between water hydrogen and oxygen isotope values of maize xylem and soil water hydrogen and oxygen isotope values with different soil thickness was mainly concentrated in the overlying soil layer. Therefore, the growth water of maize mainly came from the overlying soil layer. The greater the soil cover thickness was, the more intersection points of the two lines and the larger the distribution range of the intersection points, the larger the soil water utilization range of maize was. When the soil cover thickness was more than 40 cm, the water utilization range of maize was basically maintained within the range of 10~40 cm. Considering the maximum rainfall intensity of 190 mm/h in Fuxin city, the optimal reclamation thickness of open-pit dump in this area should be higher than 40 cm.